modules/filetype: ensure that the module does not set empty settings

When setting any filetype suboption to null (or anything else guarded by
mkIf) it's value becomes:

    { extension = null; filename = null; pattern = null; }

Account for that case in mkIf condition so that the option would not
produce empty filetype definition.

Author: stasjok

modules/filetype.nix

@@ -6,6 +6,8 @@
 }:
 with lib;
 let
+  cfg = config.filetype;
+
   filetypeDefinition = helpers.mkNullOrOption (
     with types;
     attrsOf (oneOf [
@@ -52,7 +54,9 @@ in
         pattern = filetypeDefinition "set filetypes matching the specified pattern";
       };
 
-  config.extraConfigLua = helpers.mkIfNonNull' config.filetype ''
-    vim.filetype.add(${helpers.toLuaObject config.filetype})
-  '';
+  config.extraConfigLua =
+    lib.mkIf (cfg != null && (builtins.any (v: v != null) (builtins.attrValues cfg)))
+      ''
+        vim.filetype.add(${helpers.toLuaObject cfg})
+      '';
 }

tests/test-sources/modules/filetypes.nix

@@ -38,4 +38,21 @@
       };
     };
   };
+
+  default-empty.module =
+    { config, ... }:
+    {
+      files.test = { };
+
+      assertions = [
+        {
+          assertion = builtins.match ".*vim\.filetype\..*" config.content == null;
+          message = "No vim.filetype definitions should be present in init.lua by default.";
+        }
+        {
+          assertion = builtins.match ".*vim\.filetype\..*" config.files.test.content == null;
+          message = "No vim.filetype definitions should be present in files submodules by default.";
+        }
+      ];
+    };
 }